It is well known to coat the surface of sheets with transparent glass microspheres to provide retroreflection, decoration and improved resistance to abrasion, weather and water. For example, Gebhard et al. in U.S. Pat. No. 2,326,634, teaches that maximum brilliancy in reflex-reflection is achieved in exposed lens transparent glass bead structures through use of expensive high refractive index glass beads in the range of 1.7-1.9, which lies far above the refractive index range of 1.5-1.55 of ordinary glass. No reference was made to any irregularly shaped glass particles intermixed with the beads. A reflecting binder layer was disposed under the half-exposed glass beads to achieve reflex-reflection. To make the reflex-reflecting sheet the beads were coated over a soft, tacky under cured binder which was subsequently cured, during which the beads became embedded to roughly one-half of their diameters. The beads varied in size, with the larger beads projecting out of the binder surface more than the smaller beads.
Lovell teaches in U.S. Pat. No. 3,764,455 a retroreflective surface of exposed glass beads for coating the sides of elastomeric articles such as tires by sprinkling glass beads of 50-300 micrometers on the surface of an elastomeric, pigment containing adhesive while it is still in an adhesive state. No reference was made to the refractive index of said glass beads. No reference was made to any irregularly shaped glass particles intermixed with the beads. Examples were provided using smaller beads which were lower in retroreflection because they tended to become encapsulated by the resin into which they were sprinkled.
Berg teaches in U.S. Pat. No. 3,172,942 a reflex-reflecting transfer film which is provided with a dry strippable carrier on its reflex-reflecting face for bonding a mono-layer of high refractive index glass beads to fabrics, followed by removal of the carrier to expose the surface of the embedded glass spheres. Examples were provided where the structure was made in reverse fashion upon a removable carrier, wherein the carrier had a meltable plastic coating in which the glass beads could be embedded temporarily to roughly one-half their diameters and subsequently coated with an elastomeric binder. The refractive index of the glass beads was specified to the 1.7-1.9 criteria. No reference was made to any irregularly shaped glass particles intermixed with the glass beads.
Bingham, in U.S. Pat. No. 3,758,192, taught a retroreflective sheet structure using a particular transfer method which also provided diffuse and retroreflected color by disposing a dispersion of a reflective nacreous pigment in a substantially transparent binder which contained colored pigment on the buried side of the glass beads. Bingham's examples again were focused on high refractive index glass beads of 1.9. No reference was made to any irregularly shaped glass particles intermixed with the beads. Bingham further taught in U.S. Pat. No. 3,700,305 a sheet material which used a transparent, substantially color-free vapor deposited multi-layer dielectric mirror coating on the buried side of the glass beads which would allow good color transmission of pigmented layers buried below the reflector coat. Typically, this dielectric mirror would retroreflect the color of the incident light. However, this reflector coat was also capable of retroreflective color when the dielectric layers were properly chosen and spaced to act as a visible light pass band filter.
In both Bingham and Berg, graphic images were disposed on a separate substrate by die-cutting an image from the described sheet material and separately bonding the same to a substrate. Harper, in U.S. Pat. No. 4,102,562, describes a more convenient retroreflective imaged transfer sheet wherein the beads were transferred image-wise, after printing a portion of the bead-coated transfer sheet with an ink that was also an adhesive. A transparent dielectric reflecting layer was deposited on the surface of the glass beads before printing the ink/adhesive image, so the color of the ink was visible under daytime viewing. However, this method results in no transmission of printed ink/adhesive color under retroreflective conditions. Harper's examples again used expensive high refractive index glass. Harper makes no reference to glass beads intermixed with irregularly shaped glass particles.
Olsen, in U.S. Pat. No. 5,344,705, overcame a limitation of Harper by providing a transfer image structure which would retroreflect more than one color by printing a second ink containing nacreous reflecting particles on a first transparent colored layer, followed by printing an adhesive transfer layer. Again, his specification and examples focused on expensive high refractive index glass beads. Again, Olsen makes no reference to glass beads intermixed with irregularly shaped glass particles.
Ueda, et al. discloses, in U.S. Pat. No. 4,849,265, a decorative, protective beaded sheeting with exposed glass beads, formed by disposing the beads on a flexible substrate having an adhesive thereon in a tacky state, pressing the beads into the adhesive to flatten the outer surface, and subsequently curing the same. Ueda makes no reference to glass beads intermixed with irregularly shaped glass particles. The claimed construction provides a thin, flexible over-coating which maintains the spherical shape of the surface. This surface coating over the beads is present to reduce noise and increase resistance to sliding of hard objects placed and moved thereon. This surface coating, however, covers the natural hydrophilic character of the glass surface. Thus, Ueda et al. utilizes glass beads for decoration and protection. The method of Ueda et al., however, does not lead to articles comprising low refractive index glass beads and irregularly shaped glass particles having a low friction surface of smooth tactility.